The present invention relates to an apparatus and method for interfacing an implantable hearing aid system with a patient""s auditory system, and more particularly, to a fixation apparatus and method which yields enhanced energy transfer between an implantable actuator and the ossicular chain of a patient.
Fully-implantable and semi-implantable hearing aid systems typically employ some form of actuator to stimulate the ossicular chain and/or tympanic membrane in the middle ear of a patient. By way of primary example, implantable actuators may comprise an electromechanical transducer having a vibratory member positioned to mechanically stimulate the ossicular chain via axial vibrations communicated therebetween (see e.g. U.S. Pat. No. 5,702,342).
As may be appreciated, the utilization of an implantable hearing aid actuator of the above-noted nature entails surgical positioning of the actuator within the mastoid process of a patient""s skull. Such positioning typically requires the insertion of the actuator through a hole drilled in the mastoid process. Then, a distal end of an interconnected vibratory member is located immediately adjacent to a desired location along the ossicular chain (e.g. the incus).
In conjunction with such placement, the present inventors have recognized the importance of achieving a high degree of mechanical coupling between the vibratory member of an actuator and the ossicular chain in order to optimize performance. More particularly, the inventors have recognized that mechanical coupling may be significantly enhanced by inducing tissue interconnection with a vibratory member after implantation and/or by providing a degree of lateral loading between the vibratory member and ossicular chain. In turn, energy transfer is improved, thereby enhancing a patient""s assisted hearing.
In view of the foregoing, a general objective of the present invention is to provide a hearing aid apparatus and method that improves mechanical coupling between the vibratory member of an implantable actuator and the ossicular chain of a patient.
A related objective of the present invention is to provide for improved ossicular coupling by enhancing tissue interconnection between an implantable vibratory member and the ossicular chain of a patient.
Another related objective of the present invention is to provide for improved ossicular coupling by achieving a degree of lateral loading between an implantable vibratory member and the ossicular chain of a patient.
Yet a further related objective of the present invention is to provide for improved ossicular coupling in a manner that is relatively easy and inexpensive to implement.
One or more of the above objectives and additional advantages may be realized by an inventive fixation apparatus that comprises a proximal end for interconnection to a vibratory member of an implantable hearing aid actuator and a distal end for issue interconnection with, and preferably direct physical contact with some member of the ossicular chain of a patient (e.g. the incus). The fixation apparatus further includes a body portion extending between the proximal end and the distal end.
In one aspect of the invention, the body portion of the fixation apparatus may comprise at least one surface discontinuity for inducing patient tissue attachment thereto after implantation of the fixation apparatus. Such discontinuity may be defined by surface pores and/or surface asperities and/or by one or more complex surfaces such as grooves, depressions, holes, slots, recesses or the like at the distal end or along the body portion of the fixation apparatus.
In one arrangement, the fixation apparatus may be fabricated utilizing a biocompatible material that yields surface pores and/or asperities, such pores or asperities being of a size sufficient to permit tissue infiltration after implantation. For such purposes, and by way of example only, the fixation apparatus may comprise a ceramic material (e.g. aluminumoxide), a plastic material (e.g. polytetrafluroethylene (PTFE), polyethylene or polydimethylsiloxane), or a composite material (e.g. PTFExe2x80x94carbon fiber, PTFExe2x80x94aluminumoxide, or aluminum oxidexe2x80x94zirconium). Such materials may be integrally molded into or otherwise coated over a core body to define the fixation apparatus. In the later regard, examples of preferable outer coating materials include hydroxyapatite, hydroxyapatile in an elastomeric matrix, or tricalciumphosphate with fibrigen glue.
As noted above, complex surface shapes may also advantageously define one or more surface discontinuities. In one arrangement, at least one slot may be provided which extends across the distal end and rearwardly through part of the body portion of the fixation apparatus. In a related arrangement, two transverse slots may be provided which extend from the distal end rearwardly through a part of the body portion. In an additional embodiment, a recessed ring may be defined around the body portion.
In yet a further arrangement, the body portion of the fixation apparatus may comprise one or more pairs of adjacent enlarged and reduced sections, wherein corresponding lip portions are defined therebetween. By way of example, the body portion may comprise a first frusto-conical section which proximally adjoins an adjacent reduced section (e.g., a cylindrical section), thereby defining an annular, stepped-down lip therebetween. In another arrangement, two frusto-conical sections may defined within the body portion with a reduced body section proximally located adjacent to each of the frusto-conical sections to define two corresponding lips. As may be appreciated, the utilization of configurations which define stepped-down lips from a distal end to proximal end perspective serves to enhance long term coupling since tissue growth which occurs after implantation adjacent to the lip portions will restrict undesired retraction (e.g., rearward movement) of the fixation apparatus.
In a related aspect of the present invention, the body portion of the fixation apparatus may comprise one or more tapered surfaces which angle outwardly from the distal end. Such a configuration facilitates insertion of the distal end into an opening defined at a desired location along the ossicular chain of a patient, thereby yielding an arrangement in which the distal end of the fixation apparatus may actually be seated within the ossicular opening to enhance mechanical coupling therebetween. Further, the noted arrangement facilitates removal, or disengagement, of the fixation device from the ossicular chain if so desired. Additionally, in certain arrangements a degree of outward, or lateral, loading on the sidewalls of the ossicular opening may be realized.
In yet another aspect of the present invention at least a subportion of the body portion of the fixation apparatus may be oriented so that a center axis thereof is not coaxially aligned with a center axis of an opening defined at a desired interface location along the ossicular chain of a patient. Further, at least the subportion of the body portion may comprise a material that resiliently accommodates a degree of deflection so that, upon insertion of the distal end of the fixation apparatus into the ossicular opening, the body portion contacts a sidewall of the ossicular opening and is deflected to apply an outward, or lateral, loading on the sidewalls of the ossicular opening. In this regard, it is preferable that the body portion be provided so that, during insertion of the distal end into an ossicular opening, a ratio of the axial force to radial force applied at the ossicular opening site is maintained at less than about 10 to 1; preferably with no more than about 1.2 grams of axial force being applied. In the latter regard, after inserted placement of the distal end, substantially no axial force should be applied at the ossicular opening, while application of the lateral loading force should continue, thereby yielding enhanced coupling. To achieve the desired functionality, at least the noted subportion of the fixation apparatus may comprise a material having a modulus of elasticity in tension of at least about 1xc3x97107 psi. By way of example, the subportion of the body portion may comprise a metal such as a titanium, a titanium alloy, (e.g. nickle titanium), hardened platinum (e.g. cold-worked), a platinum alloy (e.g. platinum iridium), or a gold-plated stainless steel. Of note, a metallic core body may also be utilized with a ceramic material coating for tissue attachment purposes as referenced above.
When one or more slots are provided as described above, two or more leg members may each correspondingly define deflectable distal subportions of the body portion. Further, the distal outer surfaces of each of the leg members may be tapered as noted above. More particularly, the distal end of the fixation apparatus may have a maximum cross-dimension, (i.e. diameter) that is less than the minimum cross-dimension of a defined ossicular opening, while the distal outer tapered surfaces of the leg members may combinatively define a maximum cross dimension that is greater than the maximum cross-dimension of the ossicular opening. As such, upon insertion of the distal ends of the leg members into the ossicular opening the leg members may contact the internal sidewalls and gradually deflect inward toward a center axis of the fixation apparatus to yield lateral loading for enhanced mechanical coupling. Additionally, the outer surfaces of one or more of the leg members may be defined to angle outwardly from the proximal end of the fixation apparatus to an adjoinment region with a corresponding tapered surface at the distal end. Such a configuration may be utilized to increase the magnitude of outward mechanical loading per unit distance of distal end insertion into an ossicular opening.
In yet another aspect of the present invention, at least a subportion of the body portion may comprise a shape memory material such as titanium or a titanium alloy (e.g. nickel titanium). The subportion maybe advantageously conditioned for automatic activation at temperatures above predetermined minimum body temperature. More particularly, upon activation the body subportion may be provided to change from a first configuration to a second configuration, wherein lateral loading within an ossicular opening may be readily achieved.
In one arrangement, a distal end slot may define opposing leg members in the body portion, each of which leg members comprise a shape memory material. Upon activation, the opposing leg members are conditioned to collectively change from a closed, or collapsed, V-shape configuration to an opened, or expanded, V-shape configuration. As may be appreciated, activation may be automatically realized after surgical placement as the fixation apparatus is heated to bodily temperatures.
In a related aspect of the present invention, a fixation apparatus may comprise a spring member fabricated from a shape memory material. In turn, the body portion of the fixation apparatus may be sized to receive the spring member and adapted to be deflectable from a first configuration to a second configuration upon activation of the spring member. By way of example, a shape memory spring member may be disposed within a slot extending across and rearwardly from the distal end of a fixation apparatus, wherein activation of the spring member (e.g. upon heating to bodily temperatures after surgical placement) laterally deflects opposing leg members outwardly to achieve a degree of lateral loading within an ossicular opening.
In view of the foregoing, it may be appreciated that the present invention also contemplates an inventive method for enhancing ossicular coupling of an implantable hearing aid actuator. The method includes the step of defining an opening in the ossicular chain of a patient (i.e. via laser ablation). The method further includes the step of positioning the distal end of a fixation apparatus into ossicular opening. In conjunction with such positioning the method may further entail the application of a lateral loading force by the fixation apparatus to the internal sidewalls of the defined opening to yield enhanced mechanical coupling therebetween. Alternatively and/or additionally, the method may provide for inducing tissue interconnection between a fixation apparatus and ossicular site by providing surface pores, surface asperities and/or complex surface shapes along the body portion.
As will be understood, the inventive method may utilize a fixation apparatus comprising one or more of the above-noted features. In particular, the ossicular opening may be defined to be slightly larger than the distal end of the fixation apparatus, and the body portion may comprise outer surfaces which taper outwardly from the distal end. Further, one or more slots may be provided at the distal end of the fixation apparatus so as to define two or more leg members. In turn, the inventive method may include the step of axially advancing the distal end into an ossicular opening, wherein one or more of the leg members contacts a sidewall in the opening and is deflected towards a center axis of the fixation apparatus to achieve lateral loading.
In another approach the inventive method may further provide for lateral loading at an ossicular opening site via activation of a shape memory material. For example, at least a subportion of a body portion of the fixation apparatus may be provided that is activatable at a minimum body temperature to change from a first configuration to a second configuration, wherein the body portion contacts the internal sidewalls at an ossicular opening when activated to apply a lateral loading force thereto.
In yet another approach, a shape memory spring member may be located about or within a distal end slot of the body portion of a fixation apparatus and actuated at a minimum body temperature to change from a first to second configuration. Upon activation, the spring may contact and displace the body portion to apply a lateral loading force to the internal sidewalls of an ossicular opening.
Additional aspects and advantages of the present invention will be apparent to those skilled in the art upon review of the further description that follows: